java快速读取文本文件最后一行数据内容，文本文件非常大

http://www.iteye.com/problems/42748

public static void main(String[] args) throws Exception {
    File file = new File("E:/a.txt"); // 100M  
    long start = System.currentTimeMillis();
    String lastLine = readLastLine(file, "gbk");
    long delt = System.currentTimeMillis() - start;
    System.out.println(lastLine);
    System.out.println("读取时间(毫秒):" + delt);

    file = new File("E:/b.txt");// 仅一行文字  
    start = System.currentTimeMillis();
    lastLine = readLastLine(file, "gbk");
    delt = System.currentTimeMillis() - start;
    System.out.println(lastLine);
    System.out.println("读取时间(毫秒):" + delt);
}

public static String readLastLine(File file, String charset) throws IOException {
    if (!file.exists() || file.isDirectory() || !file.canRead()) {
        return null;
    }
    RandomAccessFile raf = null;
    try {
        raf = new RandomAccessFile(file, "r");
        long len = raf.length();
        if (len == 0L) {
            return "";
        } else {
            long pos = len - 1;
            while (pos > 0) {
                pos--;
                raf.seek(pos);
                if (raf.readByte() == '\n') {
                    break;
                }
            }
            if (pos == 0) {
                raf.seek(0);
            }
            byte[] bytes = new byte[(int) (len - pos)];
            raf.read(bytes);
            if (charset == null) {
                return new String(bytes);
            } else {
                return new String(bytes, charset);
            }
        }
    } catch (FileNotFoundException e) {
    } finally {
        if (raf != null) {
            try {
                raf.close();
            } catch (Exception e2) {
            }
        }
    }
    return null;
}